AAT3142ITP-T1 AnalogicTech, AAT3142ITP-T1 Datasheet - Page 13

• Manufacturer Part Number: AAT3142ITP-T1
• Description: High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
• Manufacturer: AnalogicTech

Capacitor Selection
Careful selection of the four external capacitors C
C
time, output ripple, and transient performance. Optimum
performance will be obtained when low equivalent series
resistance (ESR) ceramic capacitors are used. In gener-
al, low ESR may be defined as less than 100mΩ. A value
of 1μF for all four capacitors is a good starting point
when choosing capacitors. If the LED current sources are
only programmed for light current levels, then the
capacitor size may be decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended
over all other types of capacitors for use with the
AAT3142. Ceramic capacitors offer many advantages over
their tantalum and aluminum electrolytic counterparts. A
ceramic capacitor has very low ESR, is lowest cost, has a
smaller PCB footprint, and is non-polarized. Low ESR
ceramic capacitors help maximize charge pump transient
response. Since ceramic capacitors are non-polarized,
they are not prone to incorrect connection damage.
Equivalent Series Resistance
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal to a
capacitor that is caused by the leads, internal connec-
tions, size or area, material composition, and ambient
temperature. Capacitor ESR is typically measured in mil-
liohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
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Ceramic Capacitor Materials
Ceramic capacitors less than 0.1μF are typically made
from NPO or C0G materials. NPO and C0G materials
have tight tolerance and are stable over temperature.
Large capacitor values are typically composed of X7R,
X5R, Z5U, or Y5V dielectric materials. Large ceramic
capacitors, greater than 2.2μF, are often available in low-
cost Y5V and Z5U dielectrics, but capacitors greater than
1μF are usually not required for AAT3142 applications.
Capacitor area is another contributor to ESR. Capacitors
that are physically large will have a lower ESR when
compared to an equivalent material smaller capacitor.
These larger devices can improve circuit transient
response when compared to an equal value capacitor in
a smaller package size.
Thermal Protection
The AAT3142 has a thermal protection circuit that will
shut down the charge pump if the die temperature rises
above the thermal limit, as is the case during a short-
circuit of the CP pin.
Charge Pump Compatibility
The three-output AAT3142 is pin-compatible with the
AAT3140, AAT3123, and AAT3113 in TSOPJW-12 pack-
ages. The AAT3142 offers an improved overall efficiency,
wider operating range, and the ability to drive high-V
type LEDs at full current. The AAT3142 is well suited for
battery-powered applications using single-cell lithium-
ion/polymer batteries and 3-series connected dry cells
(3.6V).
PRODUCT DATASHEET
AAT3142
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